1. Field of Invention
The present invention relates to ceramic reinforced and ceramic metal matrix composite articles and the processes to produce them. Specifically, the present invention relates to a process using pressure filtration for forming a ceramic article which is reinforced using organic or inorganic materials. An article having improved physical properties is produced when the organic material is removed, and the open channels are filled with a metal. The invention also relates to ceramic articles having an internal metal network throughout the composite.
The reinforced ceramic composite article and the ceramic metal matrix composite article of the present invention have a number of uses including but not limited to pump components, valve components, armor, rocket engine components, piston engine components, industrial heat exchangers, aerospace components, gas turbine engine components, blasting nozzles, gun system components, high temperature engine components, storage battery plates, biomedical implants, dental systems, coatings (impact and thermal protection), and the like.
2. Description of Related Art
Reinforced Ceramic Articles--Ceramic, metallic and polymeric materials are reinforced with either whiskers (strong single crystals with an aspect ratio (length to diameter) usually greater than 10) or strong fibers to achieve superior mechanical properties. It is generally believed that refractory ceramics reinforced with either fibers or whiskers will be required for advanced heat engines and other high temperature structural and space exploration applications.
The manufacture of these composites requires incorporating the reinforcing agent (i.e. whisker or fiber) into the matrix material, or conversely, incorporating the desired matrix material into a preform of the desired reinforcing agent. The latter method, i.e., incorporating the matrix material into a reinforcing preform, is required when a composite with either three dimensional or isotropic reinforcement is desired (as opposed to fibers/whiskers aligned in one dimension or two dimensions).
Reinforcing preforms are a self supporting fiber (or whisker) network, which usually comprise between 10 to 50 volume percent of the preform, with the remainder volume comprised of continuous void space. Reinforcement preforms can be manufactured by a number of different techniques. For example, three dimensional weaving technology has advanced to the stage where strong, continuous fibers can be woven in a variety of shapes. Discontinuous fibers and whiskers can also be "felted" to produce preform blocks which are cut into desired shapes.
Filling the void phase within the reinforcing preform without degrading the fiber/whisker material currently presents one of the greatest problems in producing composites with a refractory, ceramic matrix. Because refractory ceramics have very high melting temperatures, very few ceramics can be forced into the preform as a molten liquid without degrading the preform material as done for many metallic and polymeric matrices. The current method of incorporating the ceramic is to infiltrate the preform with a gaseous precursor that decomposes within the interior to coat and partially fill the preform with the desired ceramic. Gas infiltration must be carried out at very low pressures to avoid flow channels connecting the exterior from clogging. Because of the low pressure requirement, composite processing requires very long processing periods (of the order of days). In addition, the chemistry, composition and microstructure of the ceramic matrix is limited to those that can be produced by vapor phase deposition/reaction. Thus, the manufacture of ceramic matrix composite materials is severely limited by present processing technology.
Ceramic-Metal Composites--Ceramics presently have limited engineering applications due to their inherent brittleness and catastrophic failure. However, the fracture toughness of ceramics enhance significantly by incorporating ductile (e.g., metal) second phases into the ceramic matrix. When the ductile, metal phase is in the path of the crack, the metal deforms plastically and exerts traction on the crack surfaces which, in turn, inhibit the crack opening and hence, increases the overall toughness of the ceramic body.
At present, the major problem in toughening ceramics with ductile metals is with making the ceramic-metal composite. Useful ceramic matrices are formed with powders that must be densified at very high temperatures. A conventional method of producing metal reinforced ceramics is to mix the metal fiber with the ceramic powder and densify the powder/fiber mixture at high temperatures under an applied pressure. An applied pressure is required because the metal reinforcement constrains the densification of the ceramic powder. In this conventional method, the fiber must not melt prior to matrix densification otherwise the metal fibers lose their shape when they melt and are squeezed into the partially dense ceramic powder. The conventional method is limited to very refractory metals which do not melt prior to matrix densification. Although refractory metal fibers may not melt, two other problems are encountered, i.e.:
(a) refractory metal reinforcements lose their shape during processing by plastic deformation, and
(b) because ceramic densification periods are long, they react with the ceramic to form unwanted compounds. Thus, the present conventional methods of making ceramic/metal composites require the application of pressure to ceramic powder-metal reinforcement mixtures at high temperatures, and are, therefore, limited to refractory metals that do not react with the ceramic matrix during processing.
All references cited in this application are incorporated herein by reference, including but not limited to:
J. F. Jamet, et al., L'Aeronautique et l'Astronautique, Vol. 2/3, No. 123/124, p. 128-142 (1987); PA0 M. S. Newkirk, et al., Journal of Materials Research, Vol. 1, No., p. 81-89 (Jan./Feb., 1986). PA0 J. Jamet, U.S. Pat. No. 4,461,842, dated July 24, 1984; and PA0 J. Jamet, et al., U.S Pat. No 4,525,337, dated June 6, 1985. PA0 J. Jamet, et al., French Patent No. 2,526,785 issued Nov. 18, 1983. PA0 J. F. Jamet, et al., "Pressure Slip Casting of Ultrafine Powders A Promising Processing for Ceramic-Ceramic Composites." ICAS Procedings 1986: 15th Congress of International Council of Aeronautical Sciences, #10936, Sept. 7 to 12, 1986. PA0 (a) combining using pressure filtration, a liquid slurry of a ceramic powder, and a pyrolyzable moiety selected from:, PA0 (b) removing the liquid portion of the powder compact of step (a) under conditions effective to remove the liquid without disrupting the shape or mechanical integrity of the ceramic powder-organic moiety compact; PA0 (c) removing the pyrolyzable moiety by heating the ceramic powder-organic compact moiety at elevated temperature conditions effective to remove the organic moiety without disrupting the shape or mechanical integrity of the ceramic powder compact thus producing an interconnected network of open channels in the ceramic powder compact; PA0 (d) densifying the ceramic powder compact by heating at a temperature effective to densify the powder without eliminating the open channels; PA0 (e) heating the densified ceramic preform of step (d) to a temperature effective to prevent thermal shock when next contacted with sufficient molten metal to effectively fill the open channels; PA0 (f) optionally using increased pressure to facilitate the molten metal intrusion into the open channels; and PA0 (g) cooling the formed ceramic-metal matrix article. PA0 (a) combining a composition itself comprising, PA0 (b) filtering the composition of step (a) using pressure through a pyrolyzable moiety selected from an open cell organic polymeric foam or an organic fiber under conditions to produce a ceramic-fiber powder compact having an innerconnected organic network; PA0 (c) removing the liquid remaining in the powder compact at an effective temperature below the boiling point of the liquid without disrupting the shape or mechanical integrity of the ceramic powder-organic moiety compact; PA0 (d) removing the pyrolyzable moiety at a temperature of between about 200.degree. and 800.degree. C. under conditions effective to remove the organic moiety without disrupting the shape or mechanical integrity of the ceramic powder compact thereby producing an innerconnected network of open channels within the ceramic powder compact; PA0 (e) densifying the ceramic powder compact of step (d) by heating at between about 1000.degree. and 2100.degree. C. under conditions to densify the powder compact without eliminating the open innerconnected channels, PA0 (f) heating the densified ceramic preform of step (e) to an elevated temperature effective to prevent thermal shock when next contacted with sufficient molten metal to effectively fill the open channels; PA0 (g) contacting the heated densified preform of step (f) with heated molten metal; PA0 (h) optionally employing increased external pressure of between about 1 and 100 MPa to facilitate the intrusion of the molten metal into the open channels of the densified preform; and PA0 (j) cooling the formed ceramic-metal matrix article. PA0 (a) combining using pressure filtration a liquid slurry of a ceramic powder, and either a reinforcing carbon preform or an inorganic- preform, having percolation channels to produce a reinforced ceramic powder compact; PA0 (b) removing the liquid portion of the powder compact of step (a) under conditions effective to remove the liquid at a temperature below the boiling point of the liquid without disrupting the shape or mechanical integrity of the reinforced ceramic powder compact; and PA0 (c) strengthening the ceramic powder compact by heating at a temperature effective to densify the powder without disruption of the shape or mechanical integrity of the reinforcing particles.
Also see, for example, J. Jamet, et al., French Patent No. 2,526,785, dated Nov. 18, 1983;
A new method is necessary to form a dense ceramic which is reinforced and also a ceramic containing channels in which molten metal is infiltrated to form a desired three dimensional pattern of metal reinforcement upon cooling. The new method, as described hereinbelow, not only avoids the problems of conventional processing, but also broadens the range of different ceramic/metal composites that can be produced.